This invention relates to a process and an apparatus for producing a liquid mixture in slurry state which is formed by mixing particles of coal with a hydrocarbon oil and grinding or milling the coal particles together with the oil. The slurry-state liquid mixture thus obtained can be sprayed and burned by a burner. In a preferred embodiment of this invention, the coal particles are subjected to wet milling with a preheated hydrocarbon oil, such as fuel oil.
Heretofore, there have been various technological developments and applications relating to the production of slurry-state fluids by mixing a hydrocarbon oil, such as fuel oil obtained by distillation of crude oil, for uses such as burner fuel with a coal after it has been milled into fine powder for the purpose of obtaining a fluid mixture convenient for pipeline conveyance or of obtaining a fluid mixture of high calorific value.
In addition to its use as a fuel as mentioned above, a coal/hydrocarbon oil slurry of this character has attracted attention in view of its uses as a starting material for various chemical processes.
This coal/hydrocarbon oil slurry is required, of course, to have an unchanging quality not only in its production process but also in its states of transportion and storage. Accordingly, the requisites which this slurry must fulfil are that the coal particles thus mixed be fine particles, that they be of a specific particle size distribution, that they maintain a homogeneously dispersed state, and that sedimentation separation and coagulation lumping of the coal particles must not occur.
The conventional process for producing this liquid mixture of coal and a hydrocarbon oil has comprised, fundamentally, subjecting lumps of coal to drying and milling processes thereby to render the same into powdered coal and suitably agitating this powdered coal with a hydrocarbon oil such as fuel oil thereby to disperse the coal particles and thoroughly mix the same with the oil into a slurry state.
In the above described known technique, however, a most serious problem is the danger of dust explosion in the process of producing dry finely powdered coal from coal in the form of lumps. This danger is especially great in the processing of coal of low degree of carbonization, containing a large amount of volatile materials. Accordingly, expensive safety equipment for eliminating this danger is required, whereby the production cost becomes high, and, moreover, a high level of skill is required for carrying out the processing operation.
On the other hand, in the process of mixing and agitating finely powdered coal and a hydrocarbon oil, also, the need for special devices, an increase in the required space for equipment, and an increase in the required power cannot be avoided because of the requirement for ample shearing force and residence (retention) time. This process, moreover, has a very poor operational efficiency.
Consequently, it is very difficult to obtain in a stable manner by this process a slurry in which finely powdered coal of uniform particle size distribution is thoroughly mixed with uniform dispersion in a hydrocarbon oil.